This paper reports a study on sows to check the theory of Stolkowski which hypothesizes that mineral imbalance in the diet of the female before fertilization affects the sex ratio of the progeny. Relative excess of Na+ and K+ ions (NaK diet) would favour the birth of males, while relative excess of Ca2+ and Mg2+ ions (CaMg diet) would favour the birth of females. We carried out two successive experiments. In the first, sows were given the diet for about 34 days, the molar Na + K/Ca + Mg ratios being 2.1 for the NaK diet and 0.7 for the CaMg diet. Out of a total of 677 births, the sex ratio was 55.7 with the NaK diet and 48.3 with the CaMg diet. In the second experiment, the sows were treated for about 53 days and the molar ratios were 3.9 for the NaK diet and 0.5 for the CaMg diet. Out of a total of 869 piglets, the sex ratios were 50 and 53.5, respectively. Thus, the difference observed in experiment 1 (0.05 less than P less than 0.10), which agrees with the above mentioned theory, was reversed in experiment 2, the diet-experiment interaction being significant (P less than 0.05). Overall, the diet did not affect the sex ratio; the contradictory results of the two experiments showed no reproducible effect of dietary mineral imbalance on the sex ratio in pigs. There was also a significant diet-experiment interaction (P less than 0.05) as to litter size, and a nearly significant negative relationship between sex ratio and litter size was observed.